Update:
Dan Bessie writes, "As it happens, I own the original negative (and photo) of Einstein with the marionette, created by my uncle Harry Burnett. And contrary to comments you've received, the puppet is neither Mark Twain, nor was it Photoshopped."

Attributed to Harry Burnett while Yale Puppeteers were working in their theater, Teatro Torito, on Olvera Street in Los Angeles, California, circa 1931. The photo was taken by Harry Burnett at Cal Tech in Pasadena where Albert Einstein was teaching. Einstein saw the puppet perform at the Teato Torito and was quite amused. He reached into his jacket’s breast pocket, pulled out a letter and crumpled it up. Speaking in German, he said, “The puppet wasn’t fat enough!” He laughed and stuffed the crumpled letter up under the smock to give the puppet a fatter belly. This is a wonderful photograph that Harry treasured. Harry Burnett also kept the letter in a frame and loved to retell the story and at the end give his pixish laugh.

Einstein didn’t participate in the Manhattan Project*. He was worried enough about Germany developing the a-bomb and using it in the war that he sent the famous letter to Roosevelt, but he didn’t work on developing it. Near the end of his life he called the letter his “one great mistake”.

* I wasn’t aware of this, but apparently Vannevar Bush did ask for his advice on separating fissionable materials at one point. Einstein’s views on war were well known at the time, though, and he wasn’t trusted by the project’s leaders to not discuss it.

The puppet is Billy Connolly from 2008. Bert had obviously manipulated his theory of relativity and traveled into the future, go see a show and think Billy Connolly was a muppet and then gone back in time to take the piss out of him, leaving this photo for him to see on boingboing today… before once again manipulating his theory, and starting a rock band with Elvis next week to start rehearsals for the next season of America’s Got Talent.

This reminds me of an anecdote – I forget where I read it – Einstein was lecturing late in his life at CalTech and cut the lecture short in order to catch Beanie and Cecil. Anyone know a source for that?